search cancel

Duplicate Emails with Email Security.cloud

book

Article ID: 161444

calendar_today

Updated On:

Products

Email Security.cloud

Issue/Introduction

You are seeing duplicate copies of an email being delivered to one of your users or a third-party reports recieving duplicates of an emails from your user.

Resolution

The table lists the most likely reasons that may cause duplicate emails. 

Once you have established the nature of the problem, we can investigate if the duplication is occurring within our infrastructure.
 
Cause
Description
Troubleshooting
 
The email server is overloaded
·         If your email server is overloaded, you may need to set a limit to the amount of concurrent connections that the server accepts.
·         If the email server response is slow. Connections requests are sent until the email server replies.
·         If the server is set to do reverse DNS lookups before performing security checks, MessageLabs keeps sending the email again
·         If the message size limits is set too low, the email server can either take too long to respond or it has reached its limit. In both cases, MessageLabs resends the email.
·         You are subjected to a DOS/SPAM attack. A DOS/SPAM attack takes up all of your bandwidth, resulting in the inability to receive 
 
 
Check the available bandwidth, the email server capability and the number of connections to accept (50 is usually an acceptable number of connections.)
Out of date CISCO PIX firewall
It is a known issue. The CISCO software resets the connection if the "." and the email ending are in two different TCP packets.
The wildcard and the email ending in separate TCP packets does not match MessageLabs expected protocol 
In this instance, MessageLabs resends the email.
·         Solution 1: Upgrade the PIX software
·         Solution 2: Disable the SMTP fixup protocol in the CISCO PIX configuration so that our email servers can send emails to your email server instead of PIX acting as an intermediate relay.
 Visit the CISCO website and search for CISCO defect number CSCds90792. 
A patch exists for the PIX software, versions 5.2.4 and 5.2.5.
For newer PIX versions, we recommend that you disable "ESMTP Inspect".
 
 
POP issues
A POP server sets the email status to "downloaded" after emails have been downloaded. If the email retrieving process is interrupted, the email client restart downloading emails from the beginning
 
 
Check connectivity
Setup issues
The server is not set up to delete emails from the server after download
Check your server settings and ensure that it is set to delete emails after they have been downloaded.
 
 
Multiple sending
The sender has sent an email multiple times
Select two duplicate emails randomly and check their message IDs